Electrical network



April 14, 1936. I I G. TASKER 2,037,285 v ELECTRICAL NETWORK Filed April 17, 1933 4 Sheets-Sheet [00 I000 IQOOO uvmvrox:

A L-779mm ATTORNE S.

l l l l l h April 14, 1936. G, TASKER 2,037,285

' ELECTRICAL NETWORK Filed April 17, 1933 4 Sheets-Sheet 2 INVENTOR. HGT/751(57- I WM ATTORNEYS.

April 1936. H. s. TASKER ELECTRICAL NETWORK Filed April 17, 1935 4 Sh eets-She et s mam H6. THSKf/Z A TTORN S.

April 14, 1936.

H. G. TA K-5R 2,037,285

ELECTRICAL NETWORK Filed April 17, 19:53 4 Sheets-Sheet 4 xaB I I FREQUENCY IN V EN TOR: hf 5.7775 K15 R.

A TTORNEYS.

Patented .jApr. 14, 1936 PATENT ornca ELECTRICAL NETWORK Homer G. Taslrer, Douglaston, N. Y., assignor to United Research Corporation, Long Island City, N. Y., a corporation of Delawarev Application April 17, 1933, Serial No. 666,459

The invention relates to electrical networks, and particularly to a variable equalizer for ,con-

trolling the frequency characteristic of an am-Q plifying or transmission system.

Equalizers heretofore have had several defects,

namely; first, adjustments affected the breadth of the selected portion of the band of frequencies;

second, adjustments affected the transmission level of the remainder-of the band of frequencies,

and third, no provision was made for utilizing the same equalizer to either increase or decrease from normal transmission a selected frequency portion.

These defects are overcomeaccording to the present invention which has for an object to selectively raise or lower the transmission emciency in one portion of the frequency spectrum,

without affecting other portions, and between chosen limits. 7

According to the invention, the transmission level of a selected portion of the band of frequencies is attenuated-and continuously changed between predetermined limits of amplitude, and

Jin either sense from the attenuated level.

Figs. 3 and 5 are simplified circuit arrangements for explaining the circuit in Fig. 1.

Fig: 8 is a modification oi. the circuit arrangement in Fig. l.

Fig. .11 is a simplified circuit arrangement of the invention. i Fig. 12 is a schematic circuit of another modification of the invention. I

Referring in detail to the. drawings, Fig. 11 illustrates an elementary form of a variable equalizer according to the present invention in which'a source of voltage having a characteristic impedance provides the voltage E-l across the line iii-l5, which voltage is modified by the impedance it in shunt to the line Ml5, by the impedance ifl which is in series in one side of that line, and by the impedance is which can be variably connected by slider it to any desired point in impedance ll, and by slider M to any desired point in impedance H6. The voltage on the load terminals of the line Ml5 is represented in the drawings as E-2, although it 'will be understood that transmission mayoccur in eitherdirection. g In the case shown in Fig. 11, the frequency characteristic is modified by the elements i6, ill and l8, l6 and ill being resistances and It being a reactive impedance.

ance it serves to augment or diminish the attenuation effects of/the resistance elements it and ill by varying amounts determined by the positions of the sliders i9 and 2d, and within those frequency ranges for which the numerical magnitude of the reactive impedance i8 is comparable to, or less than, the numerical values of impedances i6 and ill.

This will be further described in connection with Fig. 1, wherein: The" transmission line is The reactive impedillustrated as comprising two vacuum tube amplifiers l and 8 connected in tandem by transformer l, .or by other suitable coupling means. The equalizer is here illustrated as directly connected in the plate circuit of amplifier i, the series resistance element ll of Fig. 11 being here illustrated as fixed resistance 2, although the latter may be variable as shown in Fig. 11. The shunt impedance of Fig. 11 is illustrated as shunt resistance 6 in Fig. 2 and the reactance represented by block it in Fig. 11 is illustrated by inductance 3, condenser d and resistance 9 which can be connectedby slider 5 to'any selected point in the shunt resistance t. The plate circuit for tube l is completed from the cathode Zito battery 22 and through the shunt resistance 6 and series resistance 2. This plate circuit could, with equal facility be isolated from these resistances by means of a transformer. The lefthand terminal of inductance a is connected to the line at'a' point between the anode of tube l and the resistance 2, although as above described, this ter minal may be connected to any desired point in resistance 2 as shown in Fig. 11.

The values of inductance 3 and condenser d are such that the branch circuit in which they are included is tuned within the frequency range which it is desired to control and which, of course,-

pertains to the frequencies transmitted by the tubes 5 and t.

The function of the equalizer in Fig. 1 may be understood in connection with Fig. 2, wherein curve A represents the frequency characteristic which would result from directly connecting the plate circuit'of vacuum tube i to the transformer l, and this curve is assumed to be substantially fiat as shown within the useful frequency range of the transformer 1. Curve B in Fig. 2 illustrates the decrease in transmission efllciency due quency while elemen are desired.

Considering now the operation resulting from the presence of the reactive elements 3 and 4 in Fig. 1, it will be apparent that the presence of these elements will change the frequency characteristic of the- -amplifler as elements 3 and 4 present an impedance which changes with fre- 2 and 6 do not. Resistance 6 is of the potentiometer type having terminals a and c and a sliding contact 5 to which elements 3, 4 and 9 are connected. Supborhood pose, for example, that resistor 9 is omitted and that inductance 3 and capacity 4 are pure reactances of such value as to be resonant at 1,000 cycles and that the reactance of either at this frequency is large compared to resistance 2. If slider 5 is-at terminal a of the resistance 0, then near the frequency of resonance (i. e.,1,000 cycles) elements 3 and 4 will provide a low impedance path around resistance 2 as, .a result of which the signal strength will be increased in the man- .ner illustrated by curve C of Fig. 2. The-result will be to emphasize the frequencies in ,the neighof 1,000cycles, leaving undisturbed the frequencies which are remote from that value. It should be noted that even with pure reactances,

' the peak of curve C will not rise higher than the level to which all frequencies would be raised if resistance 2were short-circuited. This level is shown by dotted curve D of Fig. 2. The difference between curves A and D represent the attenuation due to the shunting eifectof resistance 0.

On the other hand, when slider 5 is at terminal of resistance 6, the impedance elements I and 4 appear in shunt to the amplifying system with the result that frequencies in the neighborhood of 1,000 cycles will be greatly attenuatedwhile 1 those remote from 1,000 cycles will be aifected but slightly, as illustrated by curve E of Fig. 2.

' It is obvious that as slider moves continuously from terminal 0 to terminal a, the signal strength at 1,000 cycles will. vary continuously from the lowest point of curve E to the highest point. of curve C. Neighboring frequencies will likewise be more or less affected in a similar mar ner so that a family of curves will result, as illustrated in Fig. 4-. At some point D on resistance 0 the effect of elements 4 and 5 will pass through zero and the frequency characteristic will be the same as if 3 and 4 were disconnected. This will be readily understood from Fig. 5 in which the circuit elements are redrawn in conventional Wheatstone bridge form. The plate impedance of vacuum tube l is represented by resistances Rp which comprises in this case the characteristic impedance of the incoming line, and the other elements are as in Fig. 1: The useful voltage appears across terminals a and c of resistance 0, and with respect to the Wheatstone bridge as formed, the elements 3 and 4 comprise the equivalent galvanometer circuit.

At balance (i,e. when the ratio of resistance 2 to resistance Rp equals the ratio of portion ab to portion be of resistance 6) any current in ele- .4 were short-circuited,- as illustrated ments 3 and 4 will be so div ded in the bridge arms that it will not develop potential across the primary of transformer 1, as terminals 1 and c are at equipotential points. Consequently, the-frequencycharacteristicis unaffected by elements 3 and 4 as illustrated by curveB of Fig. 4.

The ourves of Fig. 2, in which the elements 3 and 4 are rather sharply resonant, may be found useful in practice but the method may be extended by proper choice of values of the circuit elements, to a broad range of requirements. These choices are .dependent upon elementary considerations and approximate values of circuit elements may be quickly determined.

Consider curve C of Fig. 6 which is the same as curve C of Fig. 2. Since circuit elements I and 4 of Fig. 1 are assumed to be pure reactances, the resonance peak of curve C is limited in height by resistance 2 in itsrelation to the other circuit elements.. At either side of resonance, however, the. elements 3 and 4 present a reactance which diminishes the shunting effect around resistance 2 with the result noted in curve C, where L3 is inductance of 3 and C4 is capacity of 4 and is the frequency in cycles per second. Obviously, the steepness of thiscurvewill depend on represents'the case of reactances at resonance 'much greater than resistance 2; curve K represents corresponding reactances approximating resistance 2, and curve L represents reactances quite small-compared to resistance 2.

When slider I is at terminal 0 of potentiometer 0', curves E, M and N would result from the use of reactances which in the neighborhood of resonance are respectively greater, comparable to and less than the total impedance. appearing between cathode andanode of vacuum tube l including the vacuum tube impedance and the shunting eflect of elements 2, 6 and fl.

In some of the useful applications of such an equalizer circuit, it would be objectionable to suppress any one portion of the frequency spectrum to zero as shown in curves E, Mand N, Fig. 6, and for this reason. resistor I is normally given aWalile which will limit'the lowest point of curves E, M and N to any convenient value, such] as illustrated in curves o, p and q of Fig. '7. This lowest point of the several curves will then correspond with the attenuation to which all fre-. quencies would be subjected if elements 3 and bounded by curves 8, t, u and v of Fig, 9 may be obtained by proper settings of sliders 5 and II.

It may frequently happen that it is desired to control the entire frequency spectrum bevond a by the 25 mined-by impedance values.

given point rather than a comparatively narrow r band. This-is readily accomplished by omitting one of the elements of the resonant circuit .Fig. 10 illustrates the result of omitting con-, denser 4 and inductance In from Fig. 8, assuming in this case that ,inductance I has a reactance comparable with resistor 2 in the low frequency portion of the spectrum, thereby affording curves W and BB. The resulting circuit is shown in Fig. 12.} The effect of condenser ii is illustrated in curves :1: and y for a capacity whose reactance toward the middle of the frequency-spectrum is comparable to the value of resistor 2, and curves Z and AA shows the effect of a smaller value of capacity whose reactance is comparable to thevalue of resistor 2 only at the extreme per end of the frequency spectrum. It is obvl us from the foregoing that the elements of this equalizer maybe so chosen as to accomplish a great variety of desirable results, in all of which an element of great usefulness is introduced by the use of the resistor 6 with sliding contacts 5 and I3, etc., which make it possible to continuously vary the effects produced by any of the equalizer circuits between the upper and lower limits predeter- -Having' thus described-the invention, "what is claimed as new and desired tosecure by Letters Patent, is:' I

1. The method of successively modifying the transmission level of a line for ua selective por; tion of a band of frequencies being transmitted which comprises uniformly attenuating the transmission level ofall the frequencies of said band to a predetermined level and decreasing and increasing the attenuation of said selective'portion above and below said predetermined level, the other portion of said band of frequencies remainnig at said predetermined level.

v2. The method of modifying the=transmission level of a line transmitting a band offrequencies which comprises uniformly attenuating the transmission level of all of said frequencies to a predetermined level, and increasing and de-A creasing the attenuation of a certain selective portion of said frequency; band above and 'below said predetermined level whilefmaintaining the remainder ,of said band of frequencies at said predetermined level, the limit-of increase being between the maximum level before attenuation and the predetermined level.

3. The combination of a line for transmitting a band of frequencies, attenuator means comprising a series impedance element and a shunt impedance element, whereby the signal level of said line is attenuated to a predetermined signal level, a reactive circuit effective at a selected portion of said frequency band, and means for conecting said reactive circuit across allot said series element and variably acrosssaid attenuator element. I I

4. An attenuator comprising a fixed series im-. pedance element comprising solely a resistance element and a fixed shunt impedance element, and a reactive circuit in shunt to all of said series impedance element and also in shunt to a variable portion of said shunt element.

5. The combination of a line fortransmitting,

a band .of frequencies, a fixed impedance in series in said line,an impedance in shunt-to said line, a reactive circuit having a natural frequency within the range of f said band, and means for connecting said reactive circuitlo' include in shunt therewith all of said impedance in series in the lineand an adjustable amount of said shunt impedance, whereby the transmission of a band. may be increased or decreased with re spect to uniform transmission.

6. The combination of the output electrodes of an electron discharge device, a line connected thereto for transmitting a band of frequencies, a

non-reactive impedance in series in said line, an

impedance in shunt to said line, a reactive circuit comprising inductance L", capacity C, and

.reactive circuit are in conjugate relation, one of the armsof said bridge comprising the internal output circuit impedance of an electron discharge device, the remaining arms comprising impedances of such values that said bridge in balanced relationdoes not appreciably'modify the transmission eillciency of said line and when unbal-- anced in opposite directions, increases or decreases respectively said transmission efliciency in a selected portion of the band of frequencies transmitted by said line.

8. A transmission circuit comprising a network of the Wheatstone bridge type having a transmis-' sion line and a reactive circuit in unbalanced conjugate relationship, one of the arms of said bridge comprising the internal output circuit impedance of an electron discharge device and the remaining arms of said bridge comprising non-reactive impedances respectiv ely, and means for adjustably connecting one end of said reactive circuit to diiferent points on the non-reactive impedances in adjacent arms of said bridge. I

-9. The combination of a li'ne having a series impedance and a shunt impedance for transmitting a band of frequencies, and a reactive circuit in shunt to said series impedance with adjustable connections for varying the amount of said shunt:

impedance in series with said circuit whereby the potential developed across said reactive circuit due to current from said line may in one position of adjustment add its ifect to the potential'of said line and in another position of adjustment m ay subtract its effect therefrom, whereby the transmission eillciency with respect to constant transmission over a wide band may be increased j or decreased in a selected of frequencies.

10. The combination impedance and a shunt impedance for transmitting a band of frequencies, and a reactive circuit therefor with adjustable connections to said shunt portion of said band of a line having a series' impedance whereby the potential developed across said reactive circuit due to current from said line may in one position of adjustment add its eil'ect to the potential of said line and in another posi-.-

tion of adjustment may subtract its effect therefrom, whereby the transmission emciency may be increased or decreased in a selected portion of said band of frequencies and means insaid reactive circuit for limiting theextent to which-said transmission emciency may be increased or decreased in said selected'portipn of said band of frequencies.

11. An attenuator comprising a fixed series impedance element, a fixed shunt impedance element, and a plurality of reactive circuits each having a series impedance element connectable across a portion of said shunt impedance element, the reactanceof one of said reactive circuits having a difierent sense from the reactance of another thereof.

12. The combination of a line for transmitting a band of frequencies, attenuator means comprising a series resistance and a shunt resistance for equally reducing the signal level of all frequencies in said band to a predetermined substantially constant signal level, a reactive circuit effective at a selected portion of said band of frequencies, and means for onnecting said reactive circuit in a plurality of ositions to said line and to said shunt resistance whereby in one position the transmission in said portion is increased above said predetermined level, in another'position said transmission in said selected portion is substantially unaffected by said reactive circuit, and in a third position said transmission in said selected portion is reduced below said predetermined level.

13. The combination of a line for transmitting a band of frequencies, attenuator means comprising a series impedance and a shunt impedance for equally reducing the signal level of all frequencies in said band to a predetermined substantially constant signal level, a reactive circuit effective at a selected portion of said band of frequencies, and means for connecting said reactive circuit in a plurality of positions to said line and said shunt impedance whereby in one series of positions the transmission in said selected portion is increased above said predetermined level, and in'another series of positions said transmisa,os7,aa5

sion in said selected portion is reduced below said predetermined level.

14. The method of modifying the transmission level of a line transmitting a band of frequencies which comprises uniformly attenuating the'transmission level of all of said frequencies to a predetermined level, and increasing and decreasing the attenuation "of certain selective portions "of said band of frequencies above and below'said predetermined level while. maintaining the remainder of said band of frequencies at said predetermined level.

15. A transmission circuit for a band of frequencies comprising a fixed series impedance, 9. fixed shunt impedance, said impedances uniformly attenuating all the frequencies of said band, and a plurality of reactive circuits each of which is connectable across different amounts of said shunt-impedance, each of. said reactance circuits.

increasing anddecreasing different respective selective portions of said band of frequencies in accordance with the amount of said shunt resistance connected thereto, the remaining frequencies said shunt impedance, one extreme position of said variable contact placing said reactive impedance in shunt to said fixed series resistance and the other extreme position of said variable contact placing said reactive impedance inshun to sai'dfixed shunt resistance...

HOMER G. TASKER. 

